In wireless communication systems, antenna arrays are useful to suppress multipath and interference through spatial filtering or beamforming/nulling operations. Spatial filtering or beamforming/nulling is particularly useful in networks with relatively high frequency reuse configurations, such as a frequency reuse factor of 1 or 2, where co-channel interference can be a dominant adverse effect on system performance. A goal of spatial filtering is to achieve an optimal combining, or beamforming, of the desired signals and at the same time suppress, or null out, the interference(s).
Many known spatial filtering techniques rely on knowledge of the directions of both the desired signal and the interference(s), and that the desired signal and interference have uncorrelated channels. This is hardly true in real-world system deployments. For example, in a multipath environment it is very likely that the directions of the desired signal and interference are not known and furthermore that their channels are highly correlated as a result of the multipath environment.